In processes using aqueous solutions, corrosion of metal surfaces may occur at various locations including feed lines, heaters, steam lines, process tanks and return lines. Dissolved oxygen in the water can be a principal factor influencing this corrosion, particularly where iron and steel are materials of construction. The corrosion of the iron and steel pipes, boilers, and economizers of conventional boiler systems is a well known problem; and controlling the presence of oxygen in boiler systems, particularly in the feed water section, has received considerable attention. Oxygen removal may be partially accomplished by either vacuum or thermal deaeration, or both. Complete removal of oxygen cannot be effected by these means, however, and further removal by use of a chemical scavenging agent, such as sodium sulfite, has been a customary practice.
In recent times, the use of low pressure boilers (operating below about 150 psig) has been increasingly supplemented by use of boilers operating at moderate pressure (operating between about 150 psig and about 600 psig) and high pressure (operating above about 600 psig). As boiler operating temperatures and pressures have increased there has been particular interest in the performance of oxygen scavengers at these operating conditions. For example, use of sulphites at elevated temperatures and pressures may cause an increase in solids, and formation of sulfur dioxide and hydrogen sulfide, both of which can be a source of corrosion. Scavengers such as hydrazine, hydroquinone, and certain hydroxylamines have been found to perform satisfactorily in some circumstances. In other circumstances, the efficiency with which the scavenging proceeds has not been optimal. There is thus a continuing need for alternative oxygen scavengers which can be effectively used at elevated temperatures and pressures. Of particular value are single scavenging compounds which can be used in place of hydrazine.
Despite the reported toxicity of hydrazine, much recent research has concerned development of corrosion inhibitors using hydrazine together with various organic products. Kallfass U.S. Pat. No. 3,551,349 suggests using hydrazines in combination with activating amounts of various quinone compounds (including hydroxyl forms such as pyrocatechol and hydroquinone) and their derivatives, particularly those with hydrophilic substituents such as carboxylic acid and sulphonic acid. Kaufman et al. U.S. Pat. No. 3,843,547 discloses a hydrazine-hydroxyl quinone combination in further combination with various aryl amine compounds; while Schiessel et al. U.S. Pat. No. 3,983,048 discloses a use of hydrazine along with a catalytic proportion of certain aryl amines, including sulfonated aryl amines. Noack U.S. Pat. Nos. 4,026,664 and 4,079,018 disclose hydrazine-based corrosion inhibitors which use organometallic complexes (including certain amino derivatives of carboxylic acids) as catalysts, and preferably quinone compounds (including hydroquinone) and their derivatives to render the compositions compatible with phosphonate scale control agents.
Other work has focused on nitrogen-containing compounds other than hydrazine such as various amines, hydroxylamines, or oximes. U.S. Pat. No. 4,067,690 of Cuisia et al. discloses that hydroxylamine and certain derivatives thereof are highly effective oxygen scavengers in boiler water. The hydroxylamines may be catalyzed with any of a number of well-known catalysts used in sodium sulfite or hydrazine boiler water treatment. Alakli metal hydroxide, water soluble metal salts, hydroquinone, and benzoquinone are also useful catalysts. As disclosed in Cuisia et al., U.S. Pat. No. 4,350,606 the use of a hydroxylamine compound and a volatile, neutralizing amine such as cyclohexylamine, morpholine, diethylaminoethanol, dimethylpropanolamine, or 2-amino-2-methyl-1-propanol, inhibits corrosion in boiler systems caused by carbon dioxide and oxygen. Japanese Patent Document SHO 57-204288 to Sato discloses using certain hydroxylamines as de-oxidants in combination with certain trivalent phenols, napthoquinones, and anthraquinones or various derivatives thereof, as activating agents. The invention may be practiced in boiler related systems and activity is deemed particularly significant in neutral and alkaline pH ranges. U.K. patent application No. GB 2,157,670A by Nemes et al. reveals advantageous use of hydroxylamines together with neutralizing amines and a quinone, a dihydroxybenzene, a diaminobenzene, or an aminohydroxybenzene compound to scavenge oxygen and to inhibit corrosion in boiler water and other aqueous systems.
Kerst U.S. Pat. No. 4,278,635 discloses use of various dihydroxy, diamino, and amino hydroxy benzenes and their lower alkyl substituted derivatives (including sulfonated napthalenes), and particularly hydroquinone, as deoxygenating corrosion control agents which compare favorably with other scavengers such as hydrazine. Reaction rate increases with higher pH and higher temperature are disclosed, as is use of the invention in boiler systems. Muccitelli, U.S. Pat. Nos. 4,279,767; 4,289,645; and 4,487,708, are directed to use of hydroquinone as an oxygen scavenger in combination with various compatible amines. Addition of hydroquinone to boiler feedwater together with certain neutralizing amines used to neutralize carbon dioxide in the boiler condensate system is disclosed. The systems preferably have elevated temperatures and/or alkaline conditions. European patent Publication No. 0054345 is directed to use of certain aminophenol compounds to reduce oxygen in aqueous medium such as boiler water. These scavengers are deemed to outperform hydrazine in simulated feedwater conditions and are preferably used in alkaline pH.
Weiss et al. U.S. Pat. No. 4,487,745 is directed to the use of certain oximes to remove dissolved oxygen from aqueous systems such as steam generating systems, and to thereby inhibit the corrosion of metal surfaces. Slovinsky U.S. Pat. No. 4,269,717 is directed to similar use of carbohydrazide and discloses that certain scavengers show activity comparable to hydrazine while other similar compounds do not. Cuisia U.S. Pat. No. 4,399,098 discloses use of semicarbazide and its salts as oxygen scavengers in aqueous systems such as boiler water systems to reduce corrosion from dissolved oxygen. Rothgery et al. U.S. Pat. No. 4,479,917 is directed to an oxygen-scavenging, corrosion-inhibiting agent for fluidic systems comprising certain aminoguanidine compounds. Quiggle U.S. Pat. No. 2,170,596 describes oxygen-absorbing solutions using catalysts such as amidol, para amido phenol, and certain amino-anthraquinones together with reducing agents such as sulfides.
It is well known that a nitrone may be prepared by the reaction of a hydroxylamine, particularly a mono N-substituted hydroxylamine, with an aldehyde or a ketone. It is also known that alkylation of oximes using agents such as alkyl halides or sulfates yields nitrones as well as oxime ethers, the relative yield of each depending on the reaction conditions and the nature of the reagents (including the configuration of the oxime). Murahashi et al. U.S. Pat. No. 4,596,874 describes nitrone synthesis by reacting certain secondary amines with a peroxide in the presence of a catalyst.